Cone-type loud speaker



May 24 1927. 1,630,008

M. c. HOPKINS CONE TYPE LOUD SPEAKER Filed June 1 1925 2 Sheets-Sheet 1 INVENTOR J Warn/5 C flop/H725 ATTORNEY6 May 1927' M. c. HOPKINS CONE TYPE LOUD SPEAKER Filed June 1 1925 2 Sheets-Sheet 2 /4 M 929? /5 v zgfigfz 7 x w I /4 a 2/ A;

f 12:15 if) E: I Ii] ATTORNEYS Patented May 24, 1927.

UNITED STATES PATENT OFFICE. I

IMARCZU'S C. HOPKINS, OF BROOKLYN, NEW YORK, ASSIGN OR, BY DIRECT AND MFSNE ASSIGNMENTS,

TO HOPKINS CORPORATION, A CORPORATION 01 DELAWARE.

CONE-TYPE LOUD SPEAKER.

Application filed June 1, 1925. :Serial No. 34,255.

This invention relates to electrical reproducing instruments, and more especially to loud speakers of the conical diaphragm type. A device embodying the invent-ion can be used advantageously with a radio receiving set. and also is suited to various other uses as will'be understood by those skilled in the art.

The invention is directed particularly to structural features of the conical diaphragm and of its mounting whereby there is obtained an improved operation, a structure strong mechanically, and one durable in nature and economical to manufacture.

In the preferred embodiment, the conical diaphragm is relatively stiff and light, and near. its periphery is provided with one or more reverse bends so that the diaphragm is quite free to vibrate bodily and is not subyect to excessive bending action while in use. This results in much more satisfactory and accurate tone reproduction than can be realized with diaphragms of less stiffness, and of less freedom of bodily movement.

The invention also embraces a novel supporting structure for the diaphragm. This comprises a simple and economically produced sheet metal frame to thecircular periphery of which the conical diaphragm is attached, and in the center of which an opening is provided into which the electrical mechanism for actuating the diaphragm may be inserted-the latter being removably secured to the supporting structure. The electrical mechanism or movement for actuating the diaphragm is not claimed herein. but forms the subject matter ofmy copending application Serial, No. 35,425, filed June 6, 1925. Other electrical 1nove-. ments can be used in place of the one here illustrated and described, but the latter cooperates well with this improved form of diaphragm-and its mounting, and brings out well the good sound producing characteristics of the diaphragm. The electrical arrangernent is such that the vibration of its armature. is of small amplitude. Such an arrangement is particularly suited for use with a conical diaphra-gmv which is very rigid and light in weight and restrained at the periphery as little as possible so that the diaphragm may vibrate substantially as a Whole instead of bending in the manner of an ordinary diaphragm. Although the best results are realized only with a very rigid, light and freely movable diaphragm, still fair results may be had with a. diaphragm which could not be regarded as meeting those I qualifications, and the invention should, therefore, not be construed as lim- IiZEd in those respects except insofar as such limitations are included in the appended claims. Still other features of this inventlon reside in details of construction as pointed out hereinafter.

Fig. 1 is a sectional view taken along the vertical center line of a loud speaker constructed inaccordance with this invention- Fig. 2 is a fragmentary sectional view 0 a modified form of conical diaphragm;

Figs. 3, 4 and 5 are side. top and rear views. respectively, of the electrical movement for actuating the diaphragm,"

Fig. 6 is a view partly in cross section (and on a larger scale than Figs. 3, 4 and 5) of the electrical movement;

Fig. 7 is a view partly in cross section taken along the line 77 of Fig. 6, and

Fig. 8 is a rear elevation of the back of the instrument with the electrical movement removed.

The conical diaphragm 1 is preferably of large diameter, usually more than nine inches, and generally is made wholly or in large part of paper in order that it may be of light weight. The pa er should be stiff. A long fibered paper 0 porous structure and free from loading will serve well, and any sizing should be of the fibers before felting and not of the sheet after it has been formed up. A layer of varnish or other'like material applied to a finished cone is likely to impair greatly its sound producing qualities. Brittleness in the cone is a esirable characteristic, provided the paper has at the same time sufficient toughness to withstand commercial transportation and ordinary handling during use.

It has been my experience that paper sevoral years old is better than new stock, presumably because of an increased stiffening of the fibers due to ageing. In any event, the paper used for the cone must be capable of being bent without breaking, in order that there may be formed in it the one or more peripheral creases or bends on which I rely for free bodily movement of the diaphragm when in use.

In making the diaphragm illustrated, a flat sheet of paper is first cut to form asector of the requlred radius and angle. This sector of paper is then creased oircumfen' enitally at a lesser radius or radii to mark out the line or lines on which the paper may he sharply bent to bring about the results desired by me.

During the process of forming the flat sector into a cone, those portions of the paper.

sheet which are to form the supporting brim are pressed one way or the other as the case may be so that they will assume their proper plane. The cone is then glued along its radial joint. By forming the complete cone this Way, the brim or circumferential corrugation is formed without any substantial distortion of the paper such as'might cause the main portion of the diaphragm to buckle in spots or become unequally stretched or tensioned. I I

As an alternative procedure I may cut the sector from the fiat sheetof paper and glue it to form a cone, and then by means of a suitable tool-crease the cone near its edge and crowd the periphery forward until by bending sharply at crease 2 it snaps into the osition shown in Fig. 2. Similar circum erential creasing on the lines 2' and 2 will produce the triple bend or corrugation of Fig. 1. From experience I have 'found that with a single bend as shown in Fig. 2 the forwardly flaring brim of ,the cone naturally takes up a position making the same an 1e to the vertical as does themain body o the cone. I consider this feature of importance because of the freedom from irregular strains in the. cone, and because it contributes to that freedom of bodily movement for the one which I have I found to be so vital to the most satisfactory sound production or reproduction.

By virtue of a circumferential bend or plurality of bends and the rigidity of the paper of which the dia hragm is made, the main portion of tlie diaphragm is enabled to vibrate substantially as a whole, that is to say, with little or no bending of the cone. This results in much more accurate reproduction than is possible with a diaphragm subjected to bending action; Best results are had by having. apart, but not all, of the brim of the cone secured to a supporting structure, the remaining or inner portion of the brim being relied on for flexibility in givingto the cone proper the needed support and restraint, but at the same time allowing it to move axially much as if it were without support. Any arrangement for supporting the diaphragm expensive, is attractive in appearance, and

serves its purpose well.

The supporting structure for the diaphragm and for the electrical movement or electro magnetic actuating mechanism comprises a spun or pressedsheet' metal member 3- of. frusto conical shape having an offset rimwith a beaded edge 4 formed as shown by rolling the sheet metal edge over a wire fillet. The'metal head 4 protects the edge of the cone. from mechanical injury. The brim of the diaphragm lies flat against the metal rim and is preferably cemented thereto but is enough wider than the rim to provide the desired elastic su port for the cone. The periphery of to against bead 4. The sheet metal member 3 is provided with a large central opening 5 into which the electrical movement. is removably inserted. A post 6, which may be of cast iron or brass, is riveted or otherwise secured to the sheet metal member 3 and in turn is secured to the cast metal base 7 by means of a studS and nut 9. The sheet metal member 3 is preferably provided with openings asshown at 10, 11 and 12 for the purpose of facilitating the assage of sound waves from the. inside of t e instrument to the outer air. The openings 10, 11 mental outline. The electrical movement comprises a U-shaped permanent-magnet 13, the two ends of which are slotted as indicated at 14 and 15. To one pole of the permanent magnet there is secured a soft iron pole piece 16. The pole piece 16 is secured torthe permanent magnet by means of a. screw 17. Threaded studs 18 and 19 constitute poles for the pole piece 16 andare adjustable therein, toward and away from each other. Between the arms of the pole piece 16 there is inserted a speciall formed block 20 of insulating materia, such as bakelite, having recesses of proper size to receive the electro magv net coils 21 and'22, each of which surrounds one of the studs 18 and 19. The central openings through the coils 21 and 22 are 0 the proper size to fit the unthreaded portions of studs 18 and 19. The coils 21 and 22 should be securely gripped within the block 20 and if necessary they may be cemented in place. The block 20 should make a snug fit between the arms of the pole piece 16, and the unthreaded portions of the studs 18 and 19 should lit snugly within the openings through the coils 21 and 22. A very rigid soft iron armature or reed 23 is firmly bolted at one end to one diaphragm may abut.

and 12 may beot' orna- Y pole of the permanent magnet and its free end is' normally situated midway between the ends of the poles formed by studs 18 and 19. Normally j the polarity of these poles is the same and they are so adjusted that their magnetic attractions on the armature 23 are. equal and opposing.

A rod 24 is rigidly attached at one end to the armature 23 at a point between its secured end (and that part which is disposed between the electro magnet poles. The

- other end of rod 24 is attached to the center of the diaphragm by means of a set screw 25. Rod 24 forms a connecting link between and functions to -transmit the vibrations of the armature 23 to the diaphragm 1. In order to provide a secure attachment to the center of the diaphragm, it

. is reinforced by means of a pair of conical ical vibratory diaphragm made 0 weight and stiff fibrous material having washers 26 secured together, with the diaphragm between, by means of. a hollow rivet 27through which the rod 24 extends.

Coils21 and 22 are so wound that current passing one way will cause an attrac tion of armature 23 toward one of the electro magnet poles and vice versa.

The diaphragm actuating mechanism, including permanent magnet, armature, connecting link and coils forms a self contained unit which is mounted on a metal plate 28 through the medium of a Wooden block 29 to which the permanent magnet is secured by means of a three-armed clamping plate 30, which embraces the permanent magnet, and a pair of wood screws 31. Plate 28 is secured to the sheet metal supporting member 3 by means of four machine screws 32. A lifting handle 33 is attached to plate 28 and affords a convenient means for carrying the instrument about.

This invention is capable of considerable variation and modification and should not be construed as limited to the p'articular structure described and illustrated, but only inaccordance with the appended claims.

What I claim is:

1. A loud speaker comprising a lar e conlight weight and stiff brous material with a relatively narrow peripheral portion formed by at least one forwardly projecting reverse bend disposed at an oblique angle to the axis of the cone, and supporting means for v the diaphragm engaging .said peripheral portion in the plane of a reverse bend and throughout a part only of the width of said peripheral portion.

2. A loud speaker comprising a large conical vibratory diaphragm made of light a plurality of reverse bends at the base of the cone. the outermost bend being disposed at an oblique angle with respect to theaxis of the cone, and supporting means for the dia phragm engaging said outermost bend in the plane thereof.

3. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stiff fibrous material, and a frusto-conical sheet metal supporting member having an edge portion engaging and protecting the cone at its peripheral portion.

4. A loud speaker comprising a large cons ical vibratory diaphragm made of light weight. and stiff fibrous material having a reverse bend forming a brim flaring forwardly towards the apex of the cone at an oblique angle to the axis of the cone and a support for the diaphragm located at the concave side of the cone'and having a portion engaging said forwardly flaring brim in the plane thereof.

5. A loud speaker comprising a large conical vibratory diaphragm-made of a light Weight and stiff paper, bent sharply at the base of the cone to form an outwardly flaring brim, a flaring sheet metal support for said cone secured to the outer part of said brim but leaving said cone free to vibrate substantially without distortion, and means for actuating said diaphragm, substantially as described.

6. A loud-speaker having a large conical vibratory diaphragm made of light weight fibrous material, the peripheral portion of said diaphragmbeing bent forwardly to form a flaring brim facilitating vibratory movement of said diaphragm, a structure supporting said diaphragm and having a forwardly flaring periphery to which the flaring brim of'said diaphragm is secured, and means for actuating said diaphragm.

7. The combination in a loud speaker, of a large conical diaphragm having a for warclly bent brim, a frusto-comcal sheet' metal supporting member,'the brim of said diaphragm being attached near the periphery of said supporting member and being protected thereby, said supporting member having an opening, actuating means for said diaphragm, and a plate on which said means is mounted, said plate forming a closure for i said opening being large enough to permit insertion therethrough of said actuating means.

9. A loudspeaker having a frusto-conical sheet metal supporting member with an oilset outwardly flaring rim, and a large conical vibratory diaphragm made of light weight fibrous material and having its edge glued to the rim of said supporting member.

10. In a loud speaker the combination of a frusto-conical sheet metal supporting member having a centralopening for the accom modation of actuating means, said supporting member having an offset outwardly flarin rim edged with a bead, and a large conica paper diaphragm having a forwardly 'fiaring brim seated on said rim and glued thereto, substantially as described.

11. In a loud speaker the combination of a frusto-conical sheet metal supporting member having a central opening through which actuating means may be inserted, and having other openings for the free passage of air, and a large conical diaphragm of lightweight fibrous material with a bent rim, said rim being glued to and protected by the rim of said frnsto-conical support.

12. The combination in a loud speaker of a frusto-conical support having a central opening through which actuating means may be inserted, and having other openings for the free passage of air, the periphery of said support being shaped into anoifset outwardly flaring rim edged with a bead, a large conical diaphragm of light weight fibrous material. the periphery of said diaphragm being sharply bent to form a forwardly flaring brim, said brim making substantially the same angle to the vertical as the rim of said support and being glued to said support within said bead, and actuating means carried by said support and operatively connected to said diaphra m.

13. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stiff fibrous material, and

a dished metal supporting member having an edge portion engaging and supporting the cone at its peripheral portion and having at-its center an opening through which an actuating movement can be inserted.

, 1A. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stiff fibrous material, and a dished metal supporting member having an edge portion engaging and supporting the cone at its peripheral portion.

15. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stiff fibrous material and having a circumferential crease forming a brim on which said cone may vibrate,'an d a dished metal member engaging said brim and thereby yieldingly supporting said cone, and an actuating movement housed in said dished metal member...

16. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stifi fibrous material and a sheet metal member supporting the dia phragm and having an inturned edge portion protecting the edge of the diaphragm.

17. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stiff fibrous material and a sheet metal member supporting the diaphragm and having an edge portion formed to provide an annular seat'for the edge of the cone.

18. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stifi fibrous material and a sheet metal member supporting the dia phragm, the peripheral portion of the diaphragm being secured to the peripheral portion of said supporting member and said supporting member having an inturned edge portion embracing the edge of the diaphragm.

19. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stiif fibrous material and a sheet metal back for the conical diaphragm having an inturned edge portion protecting the edge of the diaphragm.

20. In a loud speaker the combination of a large conical vibratory diaphragm made of light weight and stifl? fibrous material and a sheet metal back for the conical diaphragm having an inturned edge portion protecting the edge of the diaphragm and being provided at its center with an opening through which an actuating movement may be inserted.

21. In a loud speaker the combination of a large conical fibrous diaphragm, and a pressed sheet metal back therefor. having its edge bent to cover and protect the edge of said diaphragm.

22. In a loud speaker the combination of a large conical fibrous diaphragm, and a pressed sheet metal back therefor, said diaphragm being so mounted as to receive support from said metal back through a yielding connection.

23. In a loud sneaker the combination of a large conical fibrousdiaphragm, and a sheet metal back therefor having a central opening through which an actuating movement may be inserted into the space between the cone and its metal back.

24. In a loud speaker the combination of a large conical fibrous diaphragm, a sheet metal back therefor. actuating means housed between said diaphragm and said back, and a pedestal on which said sheet metal back is secured.

25. Ina loud speaker the combination of a large conical fibrous diaphragm, a sheet metal back therefor, actuating means housed between said diaphragm and said back, a

ponderous metal base, and means supporting said back on said base in a substantially vertical position.

26. In a loud speaker the combination of a large conical fibrous diaphragm, a sheetmetal back therefor, having a beaded periphery protecting and snpportingthe edge of said diaphragm, actuating means housed between said diaphragm and said back and a metal pedestal to which said .sheet metal 10 back is secured in a substantially vertical position.

In testimony whereof I afiix my signature.

MARCUS C. HOPKINS. 

